For a conventional image display unit such as a cathode-ray tube (CRT) or a field emission display (FED), a metal back-attached phosphor screen, which has a metal film of aluminum (Al) or the like formed on the inner surface (surface opposite to the face plate) of a phosphor layer, has been used extensively.
Such a metal film is called the metal back layer and it reflects light advancing to an electronic source, which is in light emitted from a phosphor material by electrons emitted from the electronic source, toward the face plate to enhance brightness and also serves to stabilize the potential of the phosphor layer as an anode electrode. And, the metal back also has a function to prevent the phosphor layer from being damaged by ions which are generated when gas remaining in a vacuum envelope is ionized.
The metal back layer is generally formed by a method in which a thin film of an organic resin such as nitrocellulose is formed on a phosphor layer by a spin method or the like, aluminum (Al) is vacuum-deposited thereon, and organic substances are removed by baking.
Japanese Patent Laid-Open Application No. Sho 63–102139 or the like proposes a simple method for forming a metal back layer which includes forming a metal film on a film, to which a parting agent is previously applied, by vapor deposition and transferring the metal film onto a phosphor layer with an adhesive agent.
The phosphor screen formed by a conventional method, however, had a phosphor layer 21 with large surface roughness (unevenness) as shown in a magnified form in FIG. 3A and also had largely different levels due to a difference in thickness of the phosphor layers 21 having individual colors as shown in FIG. 3B, so that a film forming property of a metal back layer thereon was poor, and the metal back layer had cracks, pinholes and the like. In the drawing, reference numeral 21a denotes phosphor particles forming the phosphor layer 21, 22 denotes a glass substrate, and 23 denotes a light absorption layer (light-shielding layer).
And, there was a disadvantage that a withstand pressure characteristic of the phosphor screen was degraded because of cracks, wrinkles, pinholes and the like of the metal back layer. It was also difficult to obtain a phosphor screen having high brightness, and particularly a display unit such as an FED operating in a low-speed electron beam area had inconsistencies in brightness.
The present invention has been made to remedy the above disadvantages and provides a method for forming a phosphor screen with the occurrence of cracks, pinholes and the like prevented by improving a film forming property of a metal back layer, and an image display unit which provides a high metal back effect, excels in a withstand voltage characteristic and can make high quality display with high brightness.